High-Temporal-Resolution Measurements of the Impacts of Ionizing Radiation on Superconducting Qubits

TL;DR

This study uses high-temporal-resolution measurements to investigate the effects of ionizing radiation on superconducting qubits, finding no direct correlation with TLS events and characterizing rapid recovery dynamics post-radiation.

Contribution

It provides the first high-resolution timing analysis of radiation impacts on superconducting qubits and clarifies the relationship between ionizing radiation and TLS scrambling events.

Findings

No correlation between TLS scrambling and radiation events.

Quasiparticle density recovers exponentially with a 13 μs time constant.

Recovery dynamics depend on niobium proximity to the qubit junction.

Abstract

We measure the effect of ionizing radiation on superconducting qubits with a timing resolution of 1 $\mu s$ using microwave kinetic inductance detectors (MKIDs) fabricated on the same substrate. We observe no correlation between two-level system (TLS) scrambling events and ionizing radiation events detected with the MKIDs, suggesting TLS scrambling events may not arise from ionizing radiation and instead the previously reported apparent correlation may be due to events without sufficient energy to trigger our MKIDs. We characterize the fast-time system recovery of transmons following a radiation event, where we observe the recovery of the enhanced qubit relaxation and excitation to be well-described by an exponential recovery to the baseline quasiparticle density, with a characteristic time of $13\pm1\ \mu$s, and a peak quasiparticle density at the junction per deposited energy of $240/\mu m^3/MeV$. The fast recovery is consistent with literature reported values for Nb-based devices with direct injection of 2$\Delta_{\text{Al}}$ phonons, demonstrating the recovery is strongly dependent on the proximity of niobium to the junction.